It is generally accepted that glucose promotes insulin release at least by two mechanisms: (1) as a signal by being attached to a still ill-definited receptor site on the cell membrane, and (2) by providing energy via the glycolytic pathway (ATP). Recent work in this laboratory suggests that glucose may play a third role, the generation of NADPH through the pentose phosphate shunt. If its activity is markedly reduced, as for example in fetal islets, or in adult islets pre-treated with 6-aminonicotinamide (an anti-metabolite of NADP and NADPH), then glucose stimulated insulin secretion is markedly attenuated. To study further the possible regulatory role of the pentose phosphate shunt in insulin release, it is proposed to employ the in vitro rat pancreatic isolated islet preparation and to examine the effect on insulin release of the following agents: 1. Methylene blue which accelerates the activity of the shunt but due to the immediate oxidation reduces the effective output of NADPH. 2. Arginine and tolbutamide as non-glucose substrates which are known to release insulin. Both will be tested with a normally functioning and pharmalogically reduced shunt to establish if their insulin releasing capacity remains intact. 3. The Pyridine Nucleotides (reduced and oxidized) to observe if they by themselves have any insulin releasing effect, and if their addition in vitro can overcome the block imposed by 6-aminonicotinamide. 4. Exogenous insulin: its negative feedback has recently been established. To search for a possible biochemical mechanism, we will measure the ratio of glucose being metabolised via the shunt and via the glycolytic pathway in the presence of high and low glucose and with and without insulin in the incubation mechanism. It is hoped that in vitro studies with these physiological and pharmaceutical agents which manipulate activity of the shunt, some light may be shed on the pathogenesis of the failing beta cell in early stages of human diabetes.